Underwater strobes : the essential component for underwater photography

Before starting , a short briefing for underwater flashes :

In photography , it’s all about light and P.O.V

Bad news , when you are diving , the deeper you go , the less light you get !

Your images will become more and more flat as you dive , with weird blue tones , without any contrasts or highlights.

Why do we encounter this phenomenon?

« The water column acts like a filter. The larger this column, the less light you will get and the less colors you get . The reds disappear from 5 meters deep, then the yellows, etc. »

Have a look at this diagram of color loss related to depth.

Underwater photo flash : how to choose a strobe for scuba diving

How to boost the quality of your underwater images ?

To capture beautiful colors and beautiful contrasts in your underwater photographs, it’s very important  to bring some artificial lights in . It’s the main role of the strobe !

“Be careful : On several forums , you can see people claiming that you can use a small light unstead of strobes.  Light beams or continous lighting will never remplace a good strobe.”


What flash should you choose ? what criteria should you trust ?

Underwater photo flash : how to choose a strobe for scuba diving

The choice  of submarine flashes is relatively small. Some criteria are to be taken into account before making your final decision:

The flash’s guide number (“GN”) :

This is the maximum range of a flash . You can calculte it by multiplying the number of the aperture to the distance at which a neutral gray object is correctly exposed !

GN = d x F

For example, an underwater flash at 100% of its power ( 1:1 ) will correctly expose a subject that is 1 m away, at F/22 .

The guide number of the flash is therefore 22. But this value also varies according to the focal length used.

“Generally, this value is calculated on shore. Underwater, the guide number is necessarily different. “

So the higher the Guide Number of a flash is, the more you will be able to illuminate a distant subject , or , use it with a narrow aperture .

It’s very usefull for environnemental pictures or images with heavy backlights .

On the other hand, for  macro photographs, the Guide Number is less important because you will never be  at 100%


The beam angle of a submarine flash

This angle varies according to the models

An open angle will be more appreciable in environemmental  photos , and will vary according to the models from 90 ° to 120 °.

Many manufacturers add diffusers to widen the angle. Note that the use of the diffuser decreases the flash output. But , on the other hand, it softens the light“.


The recycling time of the underwater flash

Very important !

A flash that takes a long time to recycle will make you miss a lot of great images .

The recycling time will vary according the the power of your flash

So that at 100% of the power , some flashes can take several secondes to be ready for another shot.

Therefore , you must anticipate this phenomenon and trigger it  at the right time. 

If you do it :

  • too early, you will regret it
  • Too late too


The color temperature of the underwater strobe

Each and every flash has it’s own color temperature .

Underwater photo flash : how to choose a strobe for scuba diving

As you can see on the graph below , the temperature that’s the closest to white ( neutral ) is right around 6000 Kelvin degrees .

Below that , these colors are called ” warm “

Above that , these colors are called ” cold “

Most flashes have a color temperature around 5000 Kelvin

The color temperature influences a lot the final result of your image .

But , it’s possible to modify the final result by balancing the white balance on your camera .


The connectivity of the underwater strobe

Underwater photo flash : how to choose a strobe for scuba diving

This also is a huge criteria that you need to have in mind before making an order.

There are 2 types of them :

  • Optical
  • Wired

Optical triggered flashes can’t be used with cameras that don’t have a built-in flash.

There is two types of wired connectivity : S5 and S6 (S6 is a high-quality connection for the TTL direct Canon devices)


What’s TTL ?

TTL means « through the lens »

In other words , the camera will communicate with the flash , and adjust it’s exposure accordingly

Inon calls TTL : « sTTL »

The off camera flash will receive informations about the internal flash’s power and adjust it’s power accordingly.

High-end cameras don’t have an internal flash : The connection is wired.

TTL is possible, but only with an S6 connection.

“Very few flash manufacturers offer a true TTL. “


E-TTL (Evaluative TTL)

This is the evaluative measure through the lens.

The measurement is coupled to the viewfinder’s collimators, the flash sends a pre-flash, the cell analyzes the light and measures the power of the flash when it will be released .



It’s exactly the same as E-TTL , but the camera also receives informations about the distance of the subject you are taking a photo of .


Positioning your underwater flashes

This is extremely important in photography , and even more in underwater photography ! The flash orientation is a hugely important criteria that will determine the final result of your image.


Use one or more flashes ?

« Of course you will need two ! »

We often start with a single flash , and it doesn’t take long before you realise that shadows look terrible , and you purchase another one to fill them.

The only solution to prevent these unpleasant shadows using a single strobe , is to put it above your camera, in the same axis as the lens .

« It’s a terrible idea , and let me tell you why !»

Your photo will often have these problems :

  1. covered with particles
  2. full of unpleasant shadows
  3. distorted by the bad  lighting.


To finish with the question of flash photography

As you can tell , a strobe is very important for every underwater photographers .

Idealy , you will need two of them so that you can get the best results possible .

Have an in-depth look at the points we covered in this article, you’d better ask yourself the right questions now .

This will allow you to chose the flash that fits your own wants and needs.